In the operation of a chlor-alkali cell sufficiently large to form commercial quantities, cell performance is partially indicated by the presence of hypochlorite. A large, industrial size electrolytic cell provides a continual discharge of electrolyte which flows out of the cell downwardly into a collection pipe for subsequent reuse. The present apparatus is a portable hypochlorite concentration meter particularly incorporating a specially devised gold electrode which measures hypochlorite concentration in the cell discharge or effluent.
Typically, there will be many cells serially connected in a commercial installation. Thus, it is necessary to monitor the performance of each cell often and one procedure for doing this is to test the percent concentration of hypochlorite in the discharge of each cell. A hypochlorite sensitive measuring device, however, encounters certain problems. For one, it is being exposed to chemically active solutions which inevitably attack the measuring device. The attack may take the form of corrosion of measuring electrodes. Another form of difficulty arises in forming a film or coating on the electrodes. When a film is formed, the electrodes have a bias as a result of the film that is formed on them. Moreover, the bias will be irregular; that is, it will change depending on moisture in the film and a number of other factors which are unpredictable. There is another source of irregularity and that relates primarily to drift from the calibration points used in setting up the system. The drift is in part a result of the factors mentioned above. As can be understood, there are many difficulties in obtaining consistent uniform measurements where the measuring instrument itself is not a source of deviation or error.
By contrast, the testing apparatus of this disclosure sets forth a system whereby accurate, repeated measurements can be obtained. Moreover, the device is able to be used often, then stored as typically will occur overnight or through the weekend, and used thereafter without drift or error arising from loss of calibration. The device is intended to be dipped into the discharge electrolyte from electrolytic cells for the purpose of measuring hypochloric concentration. It can thus be used simply by positioning the device in the discharge flow of many electrolytic cells. In fact, it is constructed and arranged so that it is easily positioned to capture the discharge flow so that the hypochlorite concentration is measured in a uniform fashion for serially connected cells. Further, the apparatus enables measurement at a uniform location with respect to the cells so that there is no bias arising from the location at which the electrolyte is measured. In part, this results from the use of an elongate probe having a funnel and cup at the bottom end, the cup capturing the discharge from the electrolytic cell. The cup has a small opening on the bottom to assure that an accumulation of electrolyte is formed in the cup. This assures that the electrodes are submerged. The electrodes are positioned in the cup so that the electrolyte submerges the electrodes.
An important feature is the incorporation of a sensing electrode which is made of gold having an etched surface area to thereby increase the surface area with a coating of hypochlorite thereon. When the device is not in use, it is preferably stored in a aqueous solution of hypochlorite to a specified concentration, thereby renewing the coating. The coating on the device is thus renewed periodically by dipping the device in the solution. This enables the coating of hypochlorite on the electrode to be renewed. This coating assures consistency in operation and thereby enables the device to measure a wide range of hypochlorite concentrations of chlor-alkali cell electrolyte.